The natural sense of hearing in human beings involves the use of hair cells in the cochlea that convert or transduce acoustic signals into auditory nerve impulses. Hearing loss, which may be due to many different causes, is generally of two types: conductive and sensorineural. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded. These sound pathways may be impeded, for example, by damage to the auditory ossicles. Conductive hearing loss may often be overcome through the use of conventional hearing aids that amplify sound so that acoustic signals can reach the hair cells within the cochlea. Some types of conductive hearing loss may also be treated by surgical procedures.
Sensorineural hearing loss, on the other hand, is caused by the absence or destruction of the hair cells in the cochlea which are needed to transduce acoustic signals into auditory nerve impulses. People who suffer from sensorineural hearing loss may be unable to derive significant benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus. This is because the mechanism for transducing sound energy into auditory nerve impulses has been damaged. Thus, in the absence of properly functioning hair cells, auditory nerve impulses cannot be generated directly from sounds.
To overcome sensorineural hearing loss, numerous cochlear implant systems—or cochlear prostheses—have been developed. Cochlear implant systems bypass the hair cells in the cochlea by presenting electrical stimulation directly to the auditory nerve fibers by way of one or more channels formed by an array of electrodes implanted in the cochlea. Direct stimulation of the auditory nerve fibers leads to the perception of sound in the brain and at least partial restoration of hearing function.
When an implantable cochlear device of a cochlear implant system is initially implanted in a patient, and during follow-up tests and checkups thereafter, it is usually necessary to fit the cochlear implant system to the patient. Fitting of a cochlear implant system to a patient is not an exact science but an ongoing trial-and-error-based iterative exercise that is largely dependent on the experience of and feedback provided by the patient. For example, in a fitting session, an audiologist or the like typically utilizes a fitting system to present various stimuli to the patient and relies on subjective feedback from the patient as to how such stimuli are perceived. Based on this process, the audiologist utilizes the fitting system to configure the cochlear implant system for operation.
A significant part of fitting the cochlear implant system to the patient includes measurement of phsycophysically-determined comfort threshold levels. For each stimulation channel of the cochlear implant system, a minimum threshold level is measured. The minimum threshold level, which is typically referred to as a “T” level, generally represents the minimum stimulation level which, when applied to a given electrode associated with the channel, produces a sensed perception of sound by the patient at least fifty percent of the time. Similarly, for each stimulation channel of the cochlear implant system, a most-comfortable threshold level is measured. The most-comfortable level, which is typically referred to as an “M” level, represents a stimulation level which, when applied to the given electrode associated with the channel, produces a sensed perception of sound by the patient that is moderately loud, or comfortably loud, but not so loud that the perceived sound is uncomfortable. Once measured, these “T” and “M” levels may be used by the fitting system in order to properly map sensed sound to stimulation levels that can be perceived by the patient as sound.
Measurement of the “T” and/or “M” levels (or other thresholds) associated with each channel of a multichannel cochlear implant system is an extremely laborious and time-intensive task. Such determinations require significant time commitments on the part of the audiologist, as well as the patient. To assist the audiologist with the measurement of the “T” and/or “M” levels (or other thresholds), the fitting subsystem typically provides a graphical user interface including an abundance of information and tools that may be used by the audiologist. For example, the graphical user interface may include multiple markers, adjustors, or other user-controllable tools that may be used by the audiologist to adjust settings such as “T” and/or “M” levels for a fitting session. In addition, during a fitting session, the fitting system may operate in a number of different operational modes that cause different and varying electrical stimulation to be applied using varying stimulation channels. Because of the amount of information and number of user-controllable tools provided in the graphical user interface, as well as the different operational modes of the fitting system, the audiologist may not always be able to readily and intuitively know precisely what stimulation levels will be used to apply electrical stimulation to a patient before the stimulation is actually applied.